Question

Explain why the voltage increases less rapidly as the DC current increases.

Answer 1

I am explaining this question for the alternator. The alternator works on the principle of electro magnetic induction.In alternator the output voltage is not proportional to DC current.

Initially the voltage varies linearly with dc current and when voltage increases to rated value the magnetic circuit will be saturated and voltage rises less steeply with dc current .So the main reason behind this is magnetic saturation.At some instant of dc current the output voltage become constant and it will not rises after this dc current value because the circuit will be saturated at that instant.This can be proved by performing OC test on alternator .The graph drawn between the voltage and dc curent gives the OCC characteristics.By observing that graph we can understand that the voltage will not rises after some instant of dc current.​​​​​this graph shows the open circuit characteristics.so finally the voltage increases less rapidly as dc current increases.